Ah, I think I know what it is, I remember now. I did have to trim out some plastic in the back of the shoulders, near the screwholes.
Fold the head up and try to close the arms over it, you should see where it needs to be trimmed.

I did that one a long time ago. I always liked the idea of modding inferno, instead of repainting towline. The body just really works for ironhide. I'm working on a ratchet right now from the same mold.